The present invention generally pertains to the delivery of ophthalmically acceptable pharmaceutically active agents to the back of the eye and more particularly to an apparatus for sub-Tenon delivery of a drug depot to the posterior segment of a human eye proximate the macula.
Several diseases and conditions of the posterior segment of the eye threaten vision. Age related macular degeneration (ARMD), choroidal neovascularization (CNV), retinopathies (e.g., diabetic retinopathy, vitreoretinopathy), retinitis (e.g., cytomegalovirus (CMV) retinitis), uveitis, macular edema, and glaucoma are several examples.
Age related macular degeneration (ARMD) is the leading cause of blindness in the elderly. ARMD attacks the center of vision and blurs it, making reading, driving, and other detailed tasks difficult or impossible. About 200,000 new cases of ARMD occur each year in the United States alone. Current estimates reveal that approximately forty percent of the population over age 75, and approximately twenty percent of the population over age 60, suffer from some degree of macular degeneration. “Wet” ARMD is the type of ARMD that most often causes blindness. In wet ARMD, newly formed choroidal blood vessels (choroidal neovascularization (CNV)) leak fluid and cause progressive damage to the retina.
In the particular case of CNV in ARMD, two main methods of treatment are currently being developed, (a) photocoagulation and (b) the use of angiogenesis inhibitors. However, photocoagulation can be harmful to the retina and is impractical when the CNV is in proximity of the fovea. Furthermore, photocoagulation often results in recurrent CNV over time. Oral administration of anti-angiogenic compounds is also being tested as a systemic treatment for ARMD. However, due to drug-specific metabolic restrictions, systemic administration usually provides sub-therapeutic drug levels to the eye. Therefore, to achieve effective intraocular drug concentrations, either an unacceptably high dose or repetitive conventional doses are required. Various implants have also been developed for delivery of anti-angiogenic compounds locally to the eye. Examples of such implants are disclosed in U.S. Pat. No. 5,824,072 to Wong, U.S. Pat. No. 5,476,511 to Gwon et al., and U.S. Pat. No. 5,773,019 to Ashton et al.
In addition, it is known to use a straight, ⅝ inch long, 25 gauge needle to perform sub-Tenon injection of corticosteroids for the treatment of posterior uveitis or macular edema associated with uveitis or anterior segment surgery. In such methods, a physician attempts to dispose the tip of the needle near the macula but without penetrating the posterior ciliary arteries or the optic nerve. However, because the physician cannot see the tip, as well as movement of the eyeball within the orbit due to contact with the straight needle, it is very difficult to precisely place the tip at the desired location near the macula. For the same reasons, it is also very difficult to determine whether the tip is correctly positioned below the Tenon's capsule. Such methods do not insure a consistent delivery of a specific quantity of drug to a region over the macula. In fact, the literature reports that only about 57 percent of injections using this method result in drug being placed in the sub-Tenon space overlying the macular area. In addition, moving a straight needle along the curved surface of the sclera causes “tenting” or stretching of the overlying Tenon's capsule. Such movement may cause penetration of the Tenon's capsule, allowing drug to be injected into surrounding tissues. Furthermore, such movement may also cause inadvertent penetration of the sclera, resulting in injection of drug into the vitreous cavity. More importantly, penetration of the sclera may result in significant damage to the eye or even a loss of sight. Documented complications of such penetrations include orbital hemorrhage, central retinal vein occlusion, and central retinal artery occlusion.
A further concern with sub-Tenon delivery of a drug depot to the posterior segment of a human eye proximate the macula is that the drug must be administered slowly and under relatively low pressure so as to be retained in the tissue rather than leaking back out of the tissue through the needle channel.
Therefore, a need exists in the field of ophthalmology for an improved apparatus for sub-Tenon delivery of a drug depot to the posterior segment of a human eye proximate the macula.